The NK sub(1) tachykinin receptor agonists, septide, Sar super(9),Met(O sub(2)) super(11)SP and Pro super(9)SP produced locomotor hyperactivity (10-20 min) when injected intracerebroventricularly (i.c.v.) in the guinea-pig. The most potent in eliciting this hyperactivity was septide (from 0.63 to 5 mu g), compared to Sar super(9),Met(O sub(2)) super(11)SP, which was active at 2.5 and 5 mu g and Pro super(9)SP which induced a non-significant increase even at 10 mu g. Wet-dog shakes were elicited by septide, Sar super(9),Met(O sub(2)) super(11)SP and Pro super(9)SP injected by the i.c.v. route in the guinea-pig. Sar super(9),Met(O sub(2)) super(11)SP, active from 0.16 to 2.5 mu g was more potent than septide (active at 1.25 mu g) and Pro super(9)SP (active at 0.63 mu g) in eliciting such behaviour. To a lesser extent, grooming was also observed after injection of these agonists. The NK sub(2) tachykinin receptor agonist, Lys super(5), MeLeu super(9), Nle super(10)NKA(4-10), up to the dose of 10 mu g i.c.v. had no effect in the guinea-pig. It neither modified locomotor activity nor induced a characteristic behavioural response. At higher doses (20 mu g), some toxic effects were noted. The NK sub(3) tachykinin receptor agonist, senktide, contrasts with the NK sub(1) receptor agonists in that it elicited only wet-dog shakes, at doses ranging from 0.32 to 1.25 mu g. It neither modified locomotor activity (1 mu g) nor induced grooming (up to 5 mu g) in the guinea-pig. To our knowledge, these results are the first demonstration that the guinea-pig could be useful to differentiate tachykinin agonists on the basis of their behavioural profile, distinct from those obtained in mice and rats.